To Test Houses vs. Hurricanes, Lab Will Simulate 155-mph Storm

As hurricane season presses on, Miami researchers are developing a new extreme technique for pinpointing how big storms damage infrastructure: Smack a full-scale, spinning test home with a Category 4 "Wall of Wind"—coconut catapult and all.

If a National Weather Service alert says that a Category 4 hurricane is headed your way, you know you can expect wind speeds of 131 to 155 mph and a storm surge up to 18 ft. above normal. What you don't know is whether your windows will blow out or if the vinyl siding is going to rip off the side of your house. So, you break out the duct tape, run to the local supply store to buy plywood and hope for the best.

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Researchers expect Atlantic hurricane seasons to intensify in coming years, and this surge in activity will inevitably lead to increased property damage. But it's proven much more difficult to predict just how hurricanes of a given strength will impact homes and buildings. Rather than wait for another Katrina to provide them with ample case studies, Stephen Leatherman and his colleagues at the International Hurricane Research Center (IHRC) in Miami are putting a full-scale hurricane inside a lab.

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The concept for the hurricane simulator--which reproduces the actual dynamics of a hurricane to identify structural weaknesses in buildings--began with a two-fan prototype that produced up to 120-mph winds and horizontal rainfall. Next, a gasoline-powered, six-fan simulator generated a wind field large enough to engulf a single-story building. Now, with $2 million in funding from the state of Florida, an array of 12 electrical fans will take the stage in early 2009.

This full-scale version of the "Wall of Wind" will pummel a test house with Category 4 or Category 5 hurricane winds and rain. The house will be mounted on a rotating turntable that will expose the structure to winds and rain from all sides. And to truly simulate the realities of a tropical storm, air cannons will propel objects like coconuts and clay roof tiles into the wind field to replicate the debris that hurls through the air during an actual event.

The earlier two-fan and six-fan versions tested model-scale buildings outside, but the new Wall of Wind will be housed inside a large hangar-type facility, which will allow for a more controlled test environment. It will also enable researchers--who will be stationed behind protective Lexan polycarbonate walls--to use high-speed video cameras and lighting to record all the action. A suite of instruments will measure and record wind speed, pressure and vertical and horizontal turbulence.

In addition to testing the durability of things like windows, soffits and roofing materials, the Wall of Wind will unleash its force on traffic signs and electrical transformers to help municipal agencies design more resistant infrastructure. "During Hurricane Wilma in 2005, Florida Power and Light Company (FPL) got a black eye because over 3 million of its customers lost power--some for as long as two weeks," Leatherman says. "So power companies have a huge stake in the testing results." In fact, FPL is installing a new substation to power the Wall of Wind's 500-hp fans.

The findings of the experiment could lead to changes in building codes for new structures and to the retrofitting of existing buildings with state-of-the-art materials. Historically, building codes have largely been based on anecdotal information collected during post-storm field inspections, but the field data was never confirmed through follow-up testing--researchers had to basically wait for the next storm to see how well new building materials performed.

In addition to more stringent building codes, Leatherman says the results could eventually lead to an improved hurricane scale--one that has more specific parameters. "We want to be able to tell people things like, 'If you live in a wood-frame house with a shingle or tile roof, here is exactly what you can expect to happen when this storm makes landfall,'" he says.

The 12-fan Wall of Wind is scheduled to be up and running by the end of the year, and the new hangar facility will be complete by September. Companies like 3M and DuPont are among the more than 50 manufacturers that plan to test their products in the facility. "We're not just here to blow houses apart," Leatherman says. "We want to test specific products to see how they perform under the worst of storm conditions."